How many atoms are on a grain of salt?

There are 2: One Sodium (Na) atom and one Chlorine (Cl) atom. This is common salt. There are many other types of salts with many different atomic structures.

Common table salt is Sodium Chloride ( NaCl ) and has no hydrogen atoms.

Salt (NaCl) is formed by ionic bonds, so it does not come in molecules. Instead, it is called a formula unit, and there are two atoms in this particular one.

6 Atoms In Total. Magnesium=1 Sulfur=1 Oxygen=4

Salt water is a mixture, not a compound, and therefore it cannot be said to have a given number of atoms because that salt to water ratio is variable.